Electrocardiography is the well-established, but still rapidly developing, science of making and studying graphic records (electrocardiograms) generated by electrical currents originating in the heart. The technology is readily applicable in both human and veterinary medicine and, while the focus of attention in the present specification will be on human medicine, it will be understood that many of the techniques described, including the present invention, are applicable in some forms of veterinary medicine as well.
An electrocardiogram (ECG) is measured through utilization of an electrocardiograph instrument, which monitors the electric potentials associated with those electric currents that transverse the heart. In practice, electrodes are positioned on the skin surface of the subject to be evaluated; those electrodes being in electrical communication with the electrocardiograph instrumentation. The electrodes must generally be such as can accurately detect and transmit electrical signals produced by various biological events. This generally requires: a large conductive surface for receipt of electrical signal; a good conductive interface between a conductor (conductive surface) and the patient; and, a secure affixation of the electrode to the subject, to avoid relative movement between the subject and the electrode during monitoring.
Electrocardiography has been applied in a variety of circumstances including: in resting diagnostic procedures; in surgical and emergency room procedures; in cardiac units; in critical care units; in ambulatory monitoring; in stress diagnostic procedures; and, more recently, in providing either continual, or intermittent, monitoring as selected for a person not under constant supervision and not substantially restrained with respect to activity. With respect to this latter application, the subject is generally provided with a portable monitor, such as a belt monitor, in electrical communication with a plurality of electrodes attached to the subject's body. An example of this is the Holter monitoring system.
Unique problems arise when the application of electrocardiography is to a subject who is expected to be monitored during more or less normal, substantially non-restricted, activity or behavior. The following list is a non-exhaustive discussion of some of these unique problems or circumstances.
1. Such subjects must be expected to undergo their normal daily routines fully clothed. Thus, the electrode system must be one such as will not be likely to be readily interfered with by clothing or the like. Further, a skin-adhesive and/or electrolyte solution or conductive adhesive utilized in association with the electrodes should be sufficiently retained (enclosed) by the electrode to inhibit likelihood of contact with the subject's clothing, for aesthetic reasons, to avoid damage to the clothing, and for comfort and convenience. Further, subjects will generally prefer arrangements which have a relatively low relief or profile, and will be thus substantially inconspicuous when worn.
2. The subject may engage in substantial movement during monitoring. To avoid interference with electrical signals measured, it is important to avoid substantial relative movement between the subject and the electrode. This generally requires an electrode which can readily flex, as the subject's body moves or twists. Further, it generally requires an arrangement which can insure a secure, relatively long-lasting, adhesion and contact between the subject's body and the electrode.
3. In use, the electrode will be attached by means of a coupler arrangement to wire leads extending into communication with the electrocardiograph. In some instances, these leads may be attached and detached a number of times during monitoring.
Several types of features and/or capabilities are desirable in arrangements well-adapted for use under such circumstances. The following list is a non-exhaustive presentation of such features and/or capabilities.
1. Preferably, the arrangement includes features which facilitate ease of good, secure, conductive connection to an electrocardiograph lead.
2. It is desirable that the device include features which facilitate connection to a monitor without application of significant deleterious stress to the adhesive interface between the electrode and the subject.
3. Preferably, features are provided which allow for a plurality of cycles of connection and disconnection, without a substantial likelihood of failure of electrode components. However, it is noted that in many home use situations, disattachment of the leads will probably be discouraged by prescribers of the procedure.
4. For good operation, it is important to provide an appropriate conductive interface between the electrode and the subject's body. In general, this is provided either by use of an electrolyte gel or through use of a conductive adhesive positioned between a conductive portion of the electrode and the subject's body. If the electrode is to be maintained in position on the subject's body, in the absence of continuous supervision by medical personnel and for a substantial length of time, it is preferred that:
a) the electrode construction be such that substantial leakage of the electrolyte gel and/or the conductive adhesive outwardly from between the subject's body and the electrode is avoided or at least substantially inhibited; and,
b) entry of foreign material, for example water or dirt, which can interfere with the electrolyte gel and/or conductive adhesive, into the interface between the electrode and the subject's body is substantially inhibited.
5. Persons wearing electrocardiograph electrodes for a substantial period of time, and during periods of normal living activity, can be expected to bring the surface of their bodies, in the vicinity of the electrodes, into contact with water. For example, the person may become wet due to weather, normal bathing activities, or spills from accidents. This can interfere with electrodes in numerous manners. For example:
a) the water could lead to signal artifact (noise);
b) the water can cause deterioration in electrode components; and,
c) the water can cause deterioration of the adhesive interface between the electrode and the person's skin, should the water leak thereto. It is preferred that the electrode be constructed in a manner resistent to such damage from water.
6. Ends of the leads attachable to the electrodes, in order to provide communication with the electrocardiograph monitor, will include electrically conductive portions at least partially exposed thereat. It is desirable to provide an arrangement in which it is unlikely that, even during subject movement, these electrically conductive portions on the leads will: come into direct contact with a subject's body; come into direct contact with electrolyte gel and/or conductive adhesive; and/or come into contact with adjacent leads and/or electrodes.
7. During normal subject movement, it can be expected that substantial tugging on the leads may occur. For example, as the subject moves or bends and the leads might be pulled tight. This may cause a tugging on the electrodes, applying stress to the adhesive interface between the electrode and the subject's body. It is desirable to provide an arrangement which substantially and efficiently avoids the likelihood that such stress will separate the electrode from the patient's body.
8. In general, it is a preferred practice to dispose of biomedical electrodes after use, particularly after an unsupervised, outpatient, use. This generally requires electrodes which can be relatively inexpensively and efficiently constructed. It is also desired that the electrodes be of a design which includes relatively inexpensive components that can be easily assembled utilizing mass manufacturing techniques.
9. It is foreseeable that subjects wearing biomedical electrodes and engaging in normal living activities may accidentally be bumped or jostled in a manner making contact between the immediate vicinity of the biomedical electrode and some foreign object. Further, a wearer of the electrode on his or her chest, may decide to lie flat on his or her stomach. It is desirable that the biomedical electrode be constructed in such a manner that it is unlikely to be damaged by such contacts or pressure. Further, it is desirable that the biomedical electrode not include hard, projecting, portions which would cause a bruise to a wearer's body, as a result of such contacts or pressure.
10. Persons wearing biomedical electrodes may be subjected to examinations such as X-ray evaluations. It is desirable that the biomedical electrode be such that it will not be likely to cause a problem shadow on a developed X-ray image, or similar image. That is, any image made by the electrode will be relatively faint and non-interfering with interpretation.
11. It can be foreseen that those portions of the electrode which are engaged by a clip or the like in communication with the monitor will be intermittently, but repeatedly, manipulated. Such manipulations of a component of the electrode can lead to a failure of the arrangement, for example by an undesired pulling at seams of the arrangement, or in similar manners. It would in general, be preferred that the biomedical electrode be designed such that manipulation of a portion thereof which is engaged by a clip or lead in communication with the monitor, is unlikely to result in an undesired or premature failure of the system.
12. Further, manipulation of portions of the electrode may tend to cause an "edge lift" effect; that is portions of the outer periphery of the electrode may be lifted from the subject's skin. This can lead to problems with: signal artifact (noise); contamination of conductive adhesive, etc. Preferably the construction of the electrode is such as will minimize, or at least inhibit, the likelihood of such edge lift.
The above list generally defines those features and capabilities it is desirable to have provided by a biomedical electrode construction. It will be understood that the list is not intended to be exhaustive, but rather it is to be interpreted as generally instructional, as to the background of biomedical electrodes. In general, a wide variety of biomedical electrodes have been provided, some of which address some or all of the above-described features and needs with varying degrees of success. No conventional biomedical electrode construction is fully satisfactory with respect to all of these problems and concerns, and improvements are continually being sought. It is an object of the present invention to provide a biomedical electrode construction which is improved over many conventional electrode arrangements, with respect to its performance in providing for the above-recited features and/or in addressing the recited problems.